Investigation of self-heating in VLSI and ULSI MOSFETs

Temperature measurements both inside and near MOSFETs were taken using special test structures. At constant bias, the temperature rise normalized with respect to the dissipated power is found to be proportional to L/sup -1/2/, where L denotes the channel length. Source-drain asymmetries of the temperature distribution were detected. The temperature rise causes a fast reduction of channel conductivity, and is pronounced for short transistors. Numerical simulations reproduce the measured high speed of the temperature rise inside MOSFETs. It is enhanced for short-channel devices and leads to an underestimation of the speed of integrated circuits. In real devices, errors in modeling delay times may therefore arise causing jitter and skew between separate signal paths. As device dimensions further scale down and the self-heating effect increases, this must be considered and eventually corrected by using the characteristics of cold transistors.<
>